1. Field of the Invention
The present invention relates to a prosthetic limb system which suspends a prosthetic limb from a residual limb stump. More particularly, it relates to a distal adaptor incorporating an air valve, or a simplified distal adaptor for use with thermoplastic sockets.
2. Description of the Related Art
It has been known to suspend a prosthetic limb from a residual limb by use of suction. In such a case, the prosthetic limb is suspended using a socket part having a proximal end shaped as a cavity into which the limb stump may be inserted. The inserted residual limb forms an airtight seal with the socket part to hold the socket part on the residual limb by suction. Air is vented from between the residual limb and the socket part during insertion of the limb and is prevented from re-entering through the socket part to maintain the vacuum. Conventional prosthetic socket parts therefore have an air valve which permits the expulsion of the air between the end of the residual limb and the socket part.
Referring to FIG. 1, a conventional prosthetic limb suspension system 400 has a socket part 402 which mounts a distal adapter 404 at its distal end 406. The distal adaptor is used to clamp a pylon or other prosthetic part to the socket part. The interior 408 of the socket part is shaped to accept a residual limb and form a seal therewith so that withdrawal of the residual limb is prevented by suction. A valve 410 is mounted in a sidewall of the socket part to permit the expulsion of air during insertion of the residual limb into the socket part.
The conventional systems, however, suffer from a number of shortcomings. One is that air is often trapped within the socket part between the valve 410 and the distal end of the socket. That is, the residual limb may cover and block the valve 410 before all of the air has been discharged during the insertion of the residual limb into the socket part, thereby reducing the suction hold effect and user comfort.
Another common problem with prosthetic limb suspension systems using air expulsion valves is that the valves are easily clogged and must be cleaned or replaced at regular intervals. With current designs, a choice must be made between ease of maintenance and optimal appearance. The valve can be made to be easily accessible for maintenance by creating an opening through the cosmetic cover of the prosthetic limb. However, most users do not like to have any discontinuities in the cosmetic finish. The other alternative with current designs is to "bury" the valve in the cosmetic cover. This makes maintenance of the valve difficult and time consuming because the cosmetic cover must be removed and later repaired or replaced.
Yet another common problem with conventional prosthetic limb suspension systems is their complexity, particularly the need in many cases to provide a two-piece socket part including an inner socket. Prosthetic socket parts are normally either laminated with a thermosetting resin or molded with a thermoplastic sheet or cone. Laminated sockets are generally of single wall construction and thermoplastic sockets are often of double wall construction. When laminating with a thermosetting resin, the distal adaptor is usually a single piece adaptor which is laminated directly to the distal end of the socket part. If using suction suspension, a valve can be laminated directly into the wall of the socket. When molding with a thermoplastic material, on the other hand, the distal adaptor generally consists of an internal piece and an external piece which are clamped together with the distal end of an outer thermoplastic socket part sandwiched between them. A second, inner thermoplastic socket part is therefore necessary to fit inside this outer thermoplastic socket part having the distal adaptor clamped thereto.
It is conventionally not considered possible to use a single thermoplastic socket part incorporating an air valve, for a number reasons. First, since the distal adaptor is attached to the distal end of the outer socket part by fastening the internal end external pieces of the distal adaptor with fasteners which pass through the wall of the outer socket part, it is difficult to provide an adequate seal where the fasteners pass through the outer socket wall. The inner socket part is therefore necessary to aid in sealing.
Second, the proximal surface of the internal adaptor piece of current distal adaptors would not be comfortable for contact with the residual limb, and so the inner socket part is required to increase user comfort.
Third, the thermoplastic property requirements for the mounting of the distal adaptor to the socket part are different from those for the incorporation of a valve into the socket part. That is, in order to provide adequate structural rigidity for attaching the distal adaptor, the thermoplastic must be relatively thick and rigid. On the other hand, the valves are conventionally molded directly into the wall of the socket part, and so the thermoplastic should be relatively thin and flexible to conform to the contours of the valves and provide an adequate seal. The designs of the valves are such that the relatively thick thermoplastic required for the attachment of the distal adaptor is too thick and rigid to provide sufficient contouring around the valve for a good seal.
The two separate socket parts, an inner socket part made from a thin flexible thermoplastic and an outer socket part made from a thicker, more rigid thermoplastic is a conventional technique for addressing this problem. However, the double wall socket system having separate inner and outer socket parts adds weight to the prosthesis and increases the labor costs in the fabrication of the prosthesis.